Users should beware of a new virus which experts say could be more destructive than the deadly Love Bug.

The polymorphic worm virus, yet another variant of the Love Bug, also uses Microsoft's Outlook to spread itself as an attachment. However, the virus randomly chooses a subject line, making it particularly difficult to detect.

Antivirus software vendor Symantec said the worm sends a mutated version of itself to all addresses in the computer user's Outlook address book, causing mail servers to clog. Additionally, once the attachment is opened, the virus overwrites numerous files and renders the computer inoperable.

The virus also randomly chooses a recently opened file from the Start/Document folder in the Microsoft Start menu and attaches it to the email as a .vbs file, said Symantec. Each time the virus spreads, it mutates itself to evade detection. This affects both local and network drives, including mapped network drives where the user has access rights.

Symantec have classed the virus as a "category four" alert, which is a "dangerous threat type that is difficult to contain". The company has five virus classifications, with one being the least severe and five being the most dangerous.

A spokesman for antivirus company F-Secure said that so far the virus does not appear to have spread as quickly as the original Love Bug, which crippled thousands of companies across the globe last month and cost businesses millions of pounds. He said this may be because people are now more wary about opening emails with attachments.